Die module for a crosshead extrusion system

ABSTRACT

An extrusion system for extruding a layer of a plastic or rubber material onto a work piece without having to continuously adjust the extrusion system during the “set-up” mode to “full-run” mode, wherein the extruded layer exhibits a predetermined cross-section size and a uniform wall gauge concentricity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 09/923,974, filedAug. 7, 2001, now U.S. Pat. No. 6,716,021B2.

BACKGROUND OF THE INVENTION

The present invention relates to an extrusion system containing a fixedcenter die module which requires no mechanical adjustments, forcontinuously extruding a molten material or a formable mass to provide atubular structure having a predetermined cross-section size and auniform wall gauge concentricity. More particularly, the presentinvention relates to a crosshead extrusion system.

Hoses made primarily of polymeric materials are widely used fortransporting various fluids such as water, gasoline, coolants, powersteering fluids, transmission fluids, etc. Typically, these hoses areused in automobiles, trucks, buses, aircraft, locomotives and watercraft to transmit such fluids. Generally, for such applications it isnecessary to provide high pressure hoses having multiple layers,including reinforcing layers, in order for the hoses to withstand thepressures and temperatures involved, and to meet the various federal andstate emission regulations, and still exhibit dimensional stability andrugged durability required for today's fuel powered internal combustionengines. For example, U.S. Pat. No. 4,330,017 to Satoh describes anautomobile fuel hose comprising a two-ply rubber tube covered with areinforcing fiber layer and further with a protective rubber layer. Thehose is constructed from a very thin inner layer of afluorine-containing rubber which is resistant to fuel, and an outerlayer of a synthetic rubber such as epichlorine rubber orethylene-acrylic rubber which is less resistant to gasoline, but issuperior in cold resistance. The extrusion system of the presentinvention can be used in the manufacture of any polymeric hose, e, g,garden hoses, air pressure hoses, and industrial hoses such as thoseused in connection with hydraulic presses and the like.

U.S. Pat. No. 5,566,720 to Cheney et al. proposes a multiple layer hosecomprising a first layer made up of a melt processible fluoroplasticterpolymer wherein the innermost surface is capable of prolongedexposure to hydrocarbon-containing fluids, and a second layer composedof a resinous thermoplastic material such as polyamide which is bondeddirectly to the outwardly oriented surface of the first layer.

U.S. Pat. No. 5,524,673 to Noone et al. describes an elongated tubingwhich includes a first layer of an extrudable, melt-processiblethermoplastic material, and a second layer of an extrudable,melt-processible thermoplastic material wherein the second layer iscapable of sufficiently permanent laminar adhesion with the first layerto prevent delamination during the desired lifetime of the tubing. Atleast one of the first and second layers is resistant to permeation ofhydrocarbons. In addition to the first and second layers, the tubingincludes a third layer adhered to the second layer.

Typically, multi-layer tubular structures are manufactured usingextrusion processes and, more particularly, using crosshead extrusionprocesses as described in U.S. Pat. No. 4,361,455 to Arterburn. Suchcrosshead extrusion systems are employed not only in the manufacture ofrubber tubes and hoses, but also for coating cylindrical work pieceswith highly viscous materials such as unvulcanized rubber as describedin U.S. Pat. No. 4,832,588 to Rasmussen, and in the manufacture ofcoated wire and cables as described in U.S. Pat. Nos. 5,183,669;5,780,066; 5,882,694; and 5,980,226 all to Guillemette; and U.S. Pat.No. 5,830,516 to McAlpine et al.

Typically, in the manufacture of rubber tubing or rubber-coated wire,the molten rubber material is extruded by means of a crosshead extrusionsystem which receives a stream of molten rubber material and causes themolten rubber material to be distributed around the circumference of awire or tube. In the present invention, the term molten is used todefine a formable mass and is not intended to specifically suggest thatthe formable rubber material is in a molten or liquid state. A varietyof crosshead devices have heretofore been known in the art formanufacturing hoses and for applying rubber coatings around thecircumference of a wire or tubular member. Furthermore, it is known inthe art to simultaneously extrude more than one layer of molten rubberto provide a multi-layer tube. Such a process is accomplished by meansof multi-layer crosshead extruder devices such as that described in U.S.Pat. No. 4,798,526 to Briggs et al. Such devices typically utilize twoor more crosshead extruders for co-extrusion of multiple layers.

It is also known in the art that it is extremely difficult to establishan even and balanced flow of molten material around the circumference ofa wire, mandrel or tube. For example, it is known that conventionalcrosshead extrusion methods pose several inherent problems such aslengthy “set-up” time which is the time spent adjusting the extruder fora desired circumferential size and uniform wall gauge concentricity.After the adjustments are made and remade several times and the “set-up”is finally complete, the material being extruded from “set-up” mode to“full run” mode has, typically, become hotter on the inside, or extrudedside, of the crosshead, thus causing concentricity of the tubularstructure to be compromised. In addition, the overheated plastic orrubber material frequently becomes discolored and exhibits otherundesirable characteristics. Furthermore, it is known that splitting andre-blending of the molten material can cause the molten material toblend together unevenly forming undesirable weld or joint lines in thefinished product. Accordingly, there is a need for an extrusion systemwhich overcomes the inadequacies and undesirable characteristics of theprior art extrusion systems.

SUMMARY OF THE INVENTION

The present invention provides a new and improved crosshead extrusionsystem wherein the crosshead extruder housing is designed to accept afixed center or non-adjustable die module which is capable of balancingthe flow of molten material to the die and maintaining this balance froma “set-up” mode to a “full-run” mode. Die modules are known, however,such die modules are notorious for requiring continuous adjustment ofthe die module in the housing in order to provide hoses havingacceptable cross-section size with a uniform wall gauge concentricity.It has now been found that a tubular member having a predeterminedcross-section size and a uniform wall gauge concentricity can beextruded in an extrusion system, particularly, a crosshead extrusionsystem which employs the die module or torpedo of the present invention.The die module of the present invention has a fixed center and requiresno mechanical adjustments while providing a balanced flow of molten orformable material to the die and maintains this balance from a “set-up”mode to a “fill-run” mode. The tubular member formed using the extrusionsystem of the present invention has a predetermined cross-section sizeand a uniform wall gauge concentricity.

A critical feature of the new crosshead extrusion system is theconstruction of a fixed center die module or “torpedo” which residesinside the extruder housing. The torpedo is designed to split the moltenmaterial coming from the screw into two substantially equal parts orcontrolled flow, and then split each of these two parts into two moresubstantially equal parts, thereby providing four substantially equalparts or controlled flow, thus allowing for a balanced volume flow tothe die. Another feature of the crosshead extrusion system is theoutside part or the body of the crosshead extruder which is designed toaccept “non adjustable” dies. Also the extruder is designed with dualcontrollable temperature zones in the front of the crosshead body tocontrol the temperature of the material flowing through the body of theextruder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the crosshead extrusion system ofthe present invention;

FIG. 2 is a perspective view of the fixed center die module of thepresent invention;

FIG. 3 is a front view of the die module of the present invention;

FIG. 4 is a right side view of the die module of the present invention;

FIG. 5 is a left side view of the die module of the present invention;

FIG. 6 is a bottom view of the die module of the present invention;

FIG. 7 is a cross-sectional view of the die module taken along line 7—7of FIG. 6;

FIG. 8 is a top view of the die module of the present invention; and

FIG. 9 is a cross-sectional view of the die module taken along line 9—9of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

Turning to the drawings, FIG. 1 illustrates a cross-sectional extrusionsystem of the present invention. The extrusion system 10 comprises ahousing 12 having a tapered interior wall surface 14, the circumferenceof the interior wall surface 14 being smaller in the front of thehousing 12 than in the rear of the housing 12. The housing 12 is adaptedwith a threaded surface 28 at the front of the housing 12 to threadedlysecure a die head (now shown) to the housing 12. As shown in FIG. 1, anextrusion module 18 is placed in the interior of the housing 12 suchthat the frusto-conical exterior surfaces 22 of the module 18 mates withthe tapered interior wall surface 14 of the housing 12. The module 18further includes wall portions 46 extending from the frusto-conicalexterior surfaces 22 of the module 18 to a tubular bore 32 havinguniform inner and outer circumferential surfaces. The tubular bore 32extends axially through module 12 for transporting a wire, mandrel, ortube (not shown) in accordance with the present invention. The module 18is secured in the housing 12 using a nut (not shown) which is threadedlylocked onto the housing 12 using threaded surface 26.

Molten material such as plastic and/or vulcanized or unvulcanized rubberis delivered under high pressure and temperature to the interior of thehousing 12 through conduit 40. The pressure and temperature employed arethose typically used in conventional extrusion systems for similarmaterial plastic or rubber materials. The molten material is distributedby diverter 38 in the fixed center die module through channels 42between raised surfaces 24 to uniformly divide the molten material intotwo substantially equal parts or equal flow. The two separate and equalparts or flow of molten material continues to be distributed forwardthrough the channels 44 wherein the two equal parts or flow of moltenmaterial are eventually uniformly divided into four equal parts ofmolten material. Finally, the four separate and equal parts of moltenmaterial are directed to tubular bore 32 where, in one aspect of theinvention, the four separate and equal parts of molten material areevenly distributed and coated onto a cylindrical body such as a hose, awire or a mandrel, to provide a tubular structure of molten materialhaving a predetermined cross-section and uniform wall gaugeconcentricity. In another aspect of the invention, the four separate andequal parts of molten material is employed to provide an unsupportedhose. In a preferred aspect of the invention, one or more temperaturecontrolling zones 20 are employed in the housing 12 to aid incontrolling the wall gauge concentricity of the extruded material. Mostpreferably, the housing 12 is constructed with dual temperaturecontrolling zones, and the temperature of the temperature controllingmedium is monitored and controlled to assure of proper temperature.

The extrusion system of the present invention can be employed in aconventional extrusion system for the extrusion of a single or multiplelayer hose using a mandrel to configure the interior circumference ofthe hose, or the extrusion system can be used in a cross-head extrusionsystem to coat wire or cable in an extrusion/coating operation. Thepresent extrusion system also can be employed to provide an unsupportedtube. The extrusion system of the present invention has been found to beparticularly useful in extruding a layer of vulcanized or unvulcanizedrubber material on a mandrel employing a cross-head extruder. The hoseis then reinforced with a reinforcing layer such as braided fiber e.g.glass fiber, polyester fiber, polyamide fiber, partially acetyl-formedpolyvinyl alcohol fiber or the like to form a high pressure hose such asthat used as a power steering hose in the automotive industry.

While the extrusion system of the present invention is shown anddescribed herein certain specific structure, it will be obvious to thoseskilled in the art that certain modifications may be made withoutdeparting from the spirit and scope of the invention concept asindicated by the scope of the appended claims.

1. A fixed center die module having a rear end and a front end for usein an extrusion apparatus through which molten material is continuouslyextruded to form a tubular structure, wherein said fixed center diemodule comprises a tubular member having a uniform inner circumferenceextending along said central longitudinal axis and a plurality of raisedsurfaces extending from said tubular member, said plurality of raisedsurfaces forming a partial outer surface of said fixed center die moduleand providing a plurality of passages between said plurality of raisedsurfaces, said partial outer surface exhibiting a frusto-conicalconfiguration tapering inward from said rear end to said front end suchthat said molten material continuously extruded therethrough is dividedinto a plurality of separate and equal portions.
 2. The fixed center diemodule of claim 1, wherein said fixed center die module furthercomprises a diverter for distributing the molten material through saidplurality of passages to uniformly divide the molten material into aplurality of separate and equal portions and provide a balanced flow ofsaid molten material.
 3. The fixed center die module of claim 2, whereinsaid diverter distributes said molten material to a first set ofpassages wherein said molten material is divided into two separate andequal portions, and subsequently urges said molten material in saidfirst set of passages to a second set of passages wherein said twoseparate and equal portions are subsequently divided into four separateand equal portions.
 4. The fixed center die module of claim 1 whereinsaid outer surface of said fixed center die module is configured to matewith an inner tapered surface of an extrususion die head to provide abalanced flow of said molten material.
 5. The fixed center die module ofclaim 4, wherein said fixed center die module is configured to evenlydistribute and coat said molten material onto a cylindrical body issuingfrom said tubular member.
 6. The fixed center die module of claim 1wherein said extrusion apparatus is a crosshead extruder.
 7. The fixedcenter die module of claim 1 wherein the configuration of said fixedcenter die module precludes the need for continuous die adjustment toachieve predetermined cross-section and uniform wall gauge concentricityof said tubular structure.
 8. A fixed center die module for use in acrosshead extrusion apparatus through which molten material iscontinuously extruded to form a tubular structure, wherein said fixedcenter die module is configured to slidably mate with a tapered interiorwall surface of a crosshead extruder housing, said fixed center diemodule comprising: a rear end; a front end; a tubular member having auniform inner circumference and an outer surface along its longitudinalaxis; a plurality of raised surfaces integral with and extending fromsaid outer surface of said tubular structure, said plurality of raisedsurfaces forming a partial outer surface exhibiting a frusto conicalconfiguration tapering inward from said rear end to said front end ofsaid fixed center die module; a plurality of passages between saidplurality of raised surfaces, said plurality of passages including afirst set of passages through which molten material is uniformly dividedinto two separate and equal portions, and a second set of passagesthrough which said two separate and equal portions are uniformly dividedinto four separate and equal portions of molten material to provide abalanced flow of molten material; and a diverter integral with andextending from said outer surface of said tubular member fordistributing said molten material to said plurality of passages, whereinsaid fixed center die module is configured to preclude the need forcontinuous die adjustment to achieve said balanced flow of moltenmaterial to an extruder die head in the manufacture of a tubularstructure having a pre-determined cross-section and uniform wall gaugeconcentricity.